It is well known that an elevator system, such as that shown in FIG. 1, comprises a controller (10) which drives an induction motor IM which drives a sheave (33). An elevator car (35) and a counterweight (36), are connected on opposite ends of a rope (34) engaged on the drive sheave (33). Usually, the weight of the counterweight (36) is selected appropriately so that it can balance a load of 40-60% of the nominal weight in the car. It is capable of reducing the maximum torque generated by the induction motor over the entire range from zero to maximum of the internal load of the car.
Referring to FIG. 2, a schematic block diagram of the elevator controller (10) without a speed detector, is shown. In particular, a known inverter circuit (2) drives the induction motor IM. AC input voltage is provided from an AC source (11) to an AC-to-DC converter 1 which converts the AC input voltage to a DC voltage which is provided across the inverter (2). A DC voltage detector (3) detects the DC voltage across the inverter circuit (2) and provides a signal indicative of the DC voltage to an A/D converter (4) and a voltage comparator.(7). The AID converter (4) converts the DC voltage to a digital signal, which is input to a control circuit or CPU (15) (which may be part of a larger control circuit or computer) for controlling the output voltage Vs to the inverter (2), as is known (details not shown and not critical to the present invention).
Also, a known regenerative power consumption circuit (8) is connected across the inverter (2). When the DC voltage across the inverter rises due to the feedback power from motor IM as the inverter enters the regenerative mode, this voltage rise is compared against a standard voltage Vd and is detected by the comparator (7) and, through drive circuit (9), the switching element of the power consumption circuit (8) is controlled and the regenerative power is consumed by resistor R1, as is known.
A frequency operation circuit (12) receives a speed command SP from a control logic 22 (discussed hereinafter) and performs a frequency calculation and provides a frequency command Fs which is provided to a frequency/voltage converter (13). The converter (13) provides an output voltage command Vs in the form of a PWM waveform indicative of the frequency command Fs. The voltage-command Vs is provided to a drive circuit (6) which drives the inverter circuit (2). The inverter circuit (2) drives the motor IM, and the elevator is operated according to the speed command (SP).
A floor arrival correction (or "re-arrival") controller (21) comprises an edge detector (23) which detects the edge of up/down door zone signals DZU, DZD (discussed hereinafter with FIG. 3) and provides detected results DZU1, DZD1 to a door zone/floor arrival control operation unit (22). The control unit (22) may contain a CPU (5) for performing some of all of the functions of the unit (22) described herein. The CPU (5) may be part of or the same as the CPU (15) described hereinbefore. The control unit (22) provides the speed command signal SP to the frequency operation circuit (12).
Referring to FIG. 3, an example of a three-floor building with door-zone sensors is shown. On each floor, a door zone sensor for upward movement (DZU) and a door zone sensor for downward movement (DZD) are arranged and provide the aforementioned DZU,DZD signals, respectively. The door zone sensors DZU,DZD are arranged offset vertically with respect to the floor position, and they also have an overlapped portion. Consequently, when the both outputs DZU, DZD are "on" (at the overlap region or "door zone"), the arrival of the car is within the prescribed error with respect to the floor position.
When, due to variation in the load in the car, e.g., due to jumping of passengers or due to entering/exiting of passengers, etc., the outputs of the two door zone sensors DZU, DZD may fail to arrive at the overlapping site at the time when the-elevator completes deceleration. In that case, the floor arrival correction (or "re-arrival") operation profile (or pattern) which is preset in the door zone/floor arrival control unit (22) is begun to perform operation for floor arrival correction.
In conventional door zone/floor arrival control operation, the direction of movement of the car is determined by the output states of the DZU and DZD door zone sensors, and the aforementioned preset floor arrival operation pattern is begun to perform floor arrival correction control. A conventional speed pattern of floor arrival is controlled as shown in FIG. 7. In particular, the direction of elevator movement, up or down, is determined from the output states of the two sensors DZU and DZD. At the point in time when both outputs of DZU and DZD sensors are on, deceleration is begun, and control is executed such that the stop position is at the central position in the door zone. In the case shown in FIG. 3, control is executed so that the car runs 15 mm after the point in time when both DZU and DZD sensors are on.
However, as the system has no speed sensor (and the system is thus in open loop operation), even when the operation pattern is started, the car may be not driven to move when the load is heavy. In this case, the frequency of the speed pattern shown in FIG. 7 may be preset to a high speed such that operation can be made even under the heaviest load. However, in that case, if the load becomes light, even when both outputs of DZU and DZD sensors are on and deceleration is begun, the car may still overrun the door zone (due to the high speed). When it is in this mode, if the position is to be corrected again, movement has to be performed in the opposite direction, and the floor arrival correction is performed repeatedly.
This problem may be solved by performing car speed detection and speed control according to whether it is a light load or heavy load, respectively. However, such a solution requires a speed detector which increases the cost of the elevator.